In general, a reciprocating compressor is to suck, compress, and discharge a gas while a piston makes a reciprocal movement within a cylinder.
FIG. 1 is a vertical-sectional view of a reciprocating compressor of a conventional art.
As shown in FIG. 1, the conventional reciprocating compressor includes a closed container 10 filled with a lubricant at its bottom and having a suction pipe (SP) and a discharge pipe (DP) communicating with each other therein, a reciprocating motor 20 fixed inside the closed container 10, a compression unit 30 installed in the closed container 10 and sucking, compressing and discharging a gas, a frame unit 40 supporting the reciprocating motor 20 and the compression unit 30, a spring unit 50 elastically supporting the armature of the reciprocating motor 20 in a movement direction and inducing a resonance, and a lubricant feed unit (not shown) mounted at the frame unit 40 and feeding a lubricant to the reciprocating motor 20 and the compression unit 30.
The reciprocating motor 20 includes a stator 21 consisting of an inner stator 21A and an outer stator 21B and an armature 22 inserted in an air gap between the inner stator 21A and the outer stator 21B and making a reciprocating movement along with a piston 31 (to be described).
The armature 22 includes a magnet support member 22A inserted in the air gap between the inner stator 21A and the outer stator 21B and combined with the piston 31 of the compression unit 30, and magnets 22B fixed at the outer circumferential surface of the magnet support member 22A at regular intervals so as to be positioned in the air gap between the inner stator 21A and the outer stator 21B.
The compression unit 30 includes the piston 31 making a reciprocal movement by being combined to the magnet support member 22A of the reciprocating motor 20, a cylinder 32 fixed at a front frame 41 (to be described) so that the piston 31 is slidably inserted thereto, and forming a compressive space 32a along with the piston 31, a suction valve 33 mounted at the front end of the piston 31, opening and closing a gas hole 31b of the piston 31 to limit suction of a gas, and discharge valve assembly 34 mounted at the front end face of the cylinder 32 to cover the compressive space and limit discharging of a compressed gas.
A gas flow passage 31a communicating with the suction pipe (SP) is formed long inside the piston 31 to a predetermined depth and a gas hole 31b is formed connected to the gas flow passage 31a, penetrating the front end face of the piston 31.
The frame unit 40 includes a front frame 41 supporting contacting the front side of the inner stator 21A and the outer stator 21B, with which the cylinder 32 is insertedly combined, a middle frame 42 supportedly contacting the rear side of the outer stator 21B, and a rear frame 43 combined with the middle frame 42 to support the rear end of an outer spring 52.
The spring unit 50 includes an inner spring 51 inserted at the outer circumference of the cylinder 32 in the axial direction so that both ends thereof are respectively supported at the front face of a combining portion of the magnet support member 22A and the piston 31 and at the corresponding inner face of the front frame 41, and an outer spring 52, both ends of which are respectively supported at the rear face of the combining portion of the magnet support member 22A and the piston 31 and a corresponding front face of the rear frame 43.
The operation of the conventional reciprocating compressor constructed as described above will now be explained.
When a power is applied to a winding coil 21C mounted at the outer stator 21B and a flux is generated between the inner stator 21A and the outer stator 21B, the armature 22 positioned at the air gap between the inner stator 21A and the outer stator 21B is moved in the flux direction to continuously make a reciprocal movement by virtue of the spring 50, and accordingly, the piston 31 combined with the armature 22 makes a reciprocal movement with the cylinder 32, so that the volume of the compressive space 32a is changed and a coolant gas is sucked into the compressive space 32a, compressed therein and discharged therefrom.
In the sucking stroke of the piston, the coolant gas is sucked into the closed container 10 through the suction pipe (SP), passes through a gas flow passage 31a and the gas hole 31b of the piston 31 and opens the suction valve 33 so as to be sucked into the compressive space 32a, and in a compression stroke of the piston, the gas is compressed to a predetermined pressure and then discharged through the discharge pipe (DP) by opening the discharge valve assembly 34. The series of processes are repeatedly performed.
However, the conventional reciprocating compressor has the following problem. That is, as shown in FIG. 2A, since the front frame 41 supporting the inner stator 21A and the outer stator 21B is closed, the compressed gas works as a flow resistance to the behavior of the armature 22 which is reciprocally moved. Thus, due to the flow resistance, the armature 22 fails to proceed to a desired position, resulting in that the stroke of the piston 31 is shortened, degrading an efficiency of the compressor.
In addition, as shown in FIG. 2B, in case where the front frame 41 supporting both the inner stator 21A and the outer stator 21B is disposed very close to the armature 22, when an overstroke of the armature 22 occurs, there is a high possibility that the armature 22 collides with the rear face of the front frame 41 to damage the magnet 22B or a flux leakage between the two stators 21A and 21B is increased. Meanwhile, in case where the front frame 41 supporting both the inner stator 21A and the outer stator 21B is disposed at a distance from the armature 22, the piston 31, the rear frame 43 and the closed container 10 should be lengthened, causing problems that the material expense of the high-priced magnet is increased, the compressor is enlarged.